This application is a continuation of application Ser. No. 680,637, filed 12/12/84.
The invention relates to a device for converting the rotary motion of an eccentric driven by a motor shaft into a reciprocating motion of a working tool coupled with a shaft pin in electrically powered appliances, in whose housing a double-armed rocker arm equipped with a shaft pin is pivotably mounted, and a connecting arm linking the double-armed rocker arm with the eccentric is provided whereby the double-armed rocker arm and the connecting arm are coupled together by an articulation, whose articulation midpoint lies on the lengthwise axis of the corresponding lever arm.
German Pat. No. 24 09 592 teaches a dry shaver with a rotary motor, an oscillating lower cutter, and a crank and rocker linkage to convert the rotary motion of the motor into the oscillating motion of the lower cutter, whereby the motor shaft is aligned parallel to the lengthwise axis of the rocker arm engaging the lower cutter and is laterally displaced by the length of the crank rod. The crank rod is connected both by an elastic gimbal suspension to the eccentric on the motor shaft and by a ball joint with the rocker arm motion. This type of motion transmission means of two differently designed and spatially separated articulation is very expensive and extremely problematical from the engineering standpoint because of the tolerances to be maintained in the bearings and articulated parts. The useful power destroyed by the motion transmission device is very high. The oscillating behavior of the rocker arm, in which a constant amplitude is deemed optimum in a predetermined rpm range of the motor, is highly negative.
Jappanese Patent Y2 57-57650 teaches a dry shaver with rotary motor, an oscillating lower cutter, and a crank and rocker linkage to convert the rotary motion of the motor into an oscillating motion of the lower cutter. The motor shaft is aligned parallel with the lengthwise axis of the rocker arm engaging the lower cutter and is disposed laterally offset by the length of the crank rod. The crank rod is made fork-shaped in the vicinity of the rocker arm, whereby the rocker arm engages this fork and is held pivotably by means of an articulation pin in the fork. The crank rod is also connected by an eccentric drive provided in the connecting rod head with the motor shaft of the rotary motor. An important disadvantage of this type of motion transmission is that the swing height of the rocker arm can only be compensated by the crank rod taking into account considerable pressure stresses and high frictional forces at the two bearing points, the articulation pin and the eccentric drive, of the crank rod, whereby a high percentage of the power to be transmitted is destroyed, and must necessarily be made up by increasing the amount of energy supplied. Increased energy consumption makes itself perceptively disadvantageous to the user of such a device by virtue of the fact that he must recharge or replace the batteries after a short period of use, for example after a small number of shaves.